Synaptotagmin 7 (Syt 7) is a Ca2+ sensor implicated in the regulation of membrane fusion in vesicular transport, but its precise role in neurons is still a matter of controversy.
Dopaminergic drugs have been shown to modulate its expression in the striatum. Here we investigate whether
dopamine receptor agonist-up-regulation of Syt 7
mRNA is specifically involved in the pathophysiological adaptations of hypersensitive striatum by analyzing other dopaminergic neurons containing brain regions. We treated rats with systemic
reserpine injections that rapidly depletes
dopamine throughout the brain, but leaves dopaminergic neurons spared from destruction. We analyzed the effects of
apomorphine, a D1 and D2 receptor agonist on Syt 7
mRNA expression in caudate putamen, nucleus accumbens, cingulate cortex, substantia nigra compacta, ventral tegmental area and hippocampus. The treatment with
reserpine resulted in akinesia,
catalepsy and rigidity and up-regulation of
proenkephalin and down-regulation of
preprotachykinin mRNA in caudate putamen, indicating a severe depletion. By acute treatment with
apomorphine proenkephalin mRNA was down-regulated and
preprotachykinin mRNA up-regulated in the caudate putamen of reserpinized rats.
Apomorphine increased Syt 7
mRNA levels only in striatum (caudate putamen and nucleus accumbens) of reserpinized rats, while in other brain regions it did not have such effect. The reserpinization and/or
apomorphine treatment had no effect on Syt 1
mRNA expression in caudate putamen. It may be concluded, that in the striatum depleted of biogene
amines, such as occurs after
reserpine treatment, the up-regulation of Syt 7 could play a specific role as part of hypersensitive response to
dopaminergic agonists.